The present invention relates to alternator assemblies, and more particularly to a one way pulley system for an alternator assembly.
It is well known in the art to use an alternator as an electricity generation mechanism for a vehicle. The rotor of the alternator is coupled to the engine of the vehicle by a belt and a belt pulley, which serve as a power transmission medium for driving the alternator to generate electric power. While the vehicle is running, the electric power generated by the alternator not only is supplied to electric equipment in the vehicle but also charges an automotive battery. The transmission belt pulley of a conventional automotive alternator is typically fastened to the rotor of the alternator with nuts such that the belt pulley is interlocked with and rotatable along with the rotor. However, when the engine accelerates or decelerates abruptly, the charging waveform of the alternator for charging the battery becomes unstable and shows significant transient variation. Meanwhile, the belt is taut on one side of the belt pulley and loose on the other side. As the loose part of the belt is under relatively low tension, a tensioner is provided thereon to adjust the belt tension. Nevertheless, when engine speed suddenly changes, the belt pulley, which is fastened with the nuts, and the belt, which is made of a flexible material, of the alternator cannot respond to the change of engine speed instantly. As a result, slippage between the belt and the belt pulley tends to occur. Moreover, while the belt experiences repeated stress from fluctuation of engine speed, the belt is also subjected to a centrifugal force generated by rotation of the belt pulley. Now that the centrifugal force varies with rotation speed of the belt pulley, the belt is often in an undesirable condition in which the belt, from a microscopic point of view, is pulled by internal tension and, from a macroscopic point of view, is flapping vigorously.
In order to prevent the transmission belt between the conventional alternator and the engine from slipping, flapping, and being unduly pulled, which are attributable to a speed difference caused by variation of rotation speed of the engine, it is known practice to provide a differential clutch device in the belt pulley of the automotive alternator, with a view to minimizing loss of transmission torque between the engine and the alternator, preventing the belt from loosening or being damaged, ensuring overall efficiency of the alternator, and avoiding noise which may otherwise result from vibration of the alternator and frequent shaking of the belt. The clutch device is configured for breaking the interlocking corotational connection between the rotor of the alternator and the belt pulley when the engine decelerates abruptly or when a brake is applied hastily. Therefore, even if the belt pulley of the alternator slows down to a low rotation speed or an idle speed, the rotor of the alternator keeps rotating because of its inertia and thus continues generating electricity. Later, due to an electromagnetic effect, governed by the Lenz's law, between the rotor and the stator of the alternator, rotation speed of the rotor gradually decreases until it is equal to that of the belt pulley, and in consequence the electric power generated by the alternator reaches a power output level matching that rotation speed. The provision of the clutch device advantageously allows an output current of the alternator to reduce slowly such that the rotor slows down progressively until it is synchronous with the belt pulley. Thus, a significant transient variation of waveform is avoided, and the alternator is protected from damage.
In principle, the foregoing belt pulley assembly with a one-way clutch function includes an outer wheel, a spindle, a clutch device, and two ball bearings. The outer wheel is axially penetrated by an insertion hole. The spindle is rotatably inserted through a central portion of the insertion hole. The clutch device is provided between the spindle and the outer wheel such that the spindle is coaxially rotatable with the outer wheel only in one direction and is left to rotate on its own if the outer wheel rotates relative to the spindle in an opposite direction. The two ball bearings are provided at a front end and a rear end of the insertion hole of the outer wheel, respectively, and mounted around the spindle.
Commercially available one-way belt pulleys for use with automotive alternators tend to have the following drawbacks in design:
1. The clutch device is formed with rolling channels having an abrupt change in its slope/depth. Hence, when the clutch device is rotating, rolling elements therein undergo excessively large radial displacement and thereby generate noise. In addition, due to improper design, connecting walls formed between the rolling channels and spring grooves fail to resolve and buffer stresses from the rolling elements.
2. The ball bearings and the belt pulley are not properly assembled. Therefore, when the belt pulley rotates at high speed, the ball bearings move axially and unstably, or balls in the ball bearings that are in contact with rolling surfaces of an inner race and of an outer race are subjected to excessive radial loading and thus cause the rolling surfaces to flake. Furthermore, the bearings generate considerable heat when rotating at high speed. When grease inside the bearings melts and evaporates, the balls and the rolling surfaces begin to seize, thus damaging the ball bearings and generating noise. Even more seriously, the high heat, once conducted to the clutch device, may melt grease therein and accelerate wear and tear thereof.
3. There is no positioning structure on an inner periphery of the belt pulley that can serve as an axial reference during assembly, nor any structure that can prevent the clutch device from axial displacement. Consequently, not only is it difficult to position components inside the belt pulley, but also the clutch device may displace axially or askew when rotating at high speed, thus impairing the overall precision of operation.
In view of the aforementioned drawbacks, an improved one-way pulley system for an alternator assembly is needed.